Colorectal cancer (CRC) is a major cause of morbidity and mortality and is the result of well characterized genetic aberrations. However, there are additional factors that modulate malignant progression and response to therapy. A large number of solid tumors contain areas of hypoxia as a result of defective tumor vasculature and poor perfusion. Hypoxia activates adaptive gene expression programs, regulating crucial biological processes including proliferation, metabolism, and metastasis. The presence of hypoxia and associated features is an adverse prognostic factor in a number of cancer types, and strategies are being developed to either overcome hypoxia or target hypoxic physiology therapeutically. Hypoxia-Inducible Lipid Droplet Associated Protein (HILPDA) is a stress-induced gene, encoding for a protein shown to localize to lipid droplets. HILPDA transcripts are highly expressed in CRC specimens but the protein's functional importance or its relation to other clinical parameters is not known. We have generated a genetically engineered mouse model where the HILPDA gene was disrupted and was replaced by the firefly Luciferase gene. This knockout/reporter mouse strain will be used to investigate colorectal oncogenesis. We hypothesize that HILPDA is a positive modulator of malignant progression by impacting colonic epithelial and stromal cell responses to oncogenic signals. Additionally, an in vitro model of adipogenesis will be used to identify HILPDA protein functional domains. We propose these investigations in 3 specific aims: 1) We will investigate the role of HILPDA in vivo in two murine models of CRC: a) in inflammation-associated carcinogenesis induced by treatment with Azoxymethane and Dextran Sodium Sulfate and b) in the context of APC inactivation by breeding the APC Min nonsense allele into our strain. Tumor incidence and multiplicity will be kinetically measured and the spectrum of lesions will be pathologically evaluated in both models. 2) Protein expression of HILPDA will be validated as a biomarker of more aggressive disease in human CRC specimens. 3) We will also identify HILPDA functional domains that can rescue the adipogenesis defects and deficiency of lipid droplets of KO cells in vitro. These HILPDA domains will then be functionally tested in transplantable tumors. These studies will determine the significance of HILPDA in CRC malignant progression and generate reagents for the mechanistic analysis of HILPDA function.